1. Field of the Invention
The invention relates in general to a recording system for video signals which are transmitted through a transmission line which has limited bandwidth.
2. Description of the Prior Art
FIG. 1 illustrates a prior art system wherein an input terminal 101 receives an input signal which is connected to a time base compressor 2 which supplies an output to a recording amplifier 108 which supplies a signal to record/playback switch 9 that is connected to a rotary head 10 of a recorder to record the signal on a tape 11a. During reproduction, a signal is reproduced from the tape 11 by the rotary head 10 and is supplied through switch 9 which is placed in the reproduction position to supply the signal shown in FIG. 18D to a time base expander 113 which supplies an output through TB1 circuit 118 to an output terminal 119. A sync amp 103, a PLL 104 and control 105 are connected between input terminal and time base compressor 102. A sync separator 114 and control 117 are connected between the switch 9 and time base expander 113. The prior art circuit is subject to jitter.
When video signals having wide band are recorded and reproduced by using an existing video tape recording mechanism if the video signal is supplied to the video tape recorder in its original form, the carrier of, for example, FM recording will be increased which deteriorates the C/N ratio and the S/N ratio.
If the rotation of the rotary head is made to be twice its normal speed so as to increase the relative speed between the head and the tape, a video signal of wide band can be recorded. For this case, since the heads are switched at, for example, the center of the vertical direction of the picture screen, if the characteristics of the head are unbalanced the quality of the picture will be changed in the upper and lower positions of the picture screen so that the picture is substantially degradated.
In the prior art, when the video signal having wide band is recorded and reproduced by the above-described methods, there occurs a problem that a good picture cannot be obtained.
When there is a luminance signal Y illustrated, for example, in FIG. 18A and chrominance signals C.sub.1 and C.sub.2 of two systems as illustrated in FIGS. 18B and 18C, it is known as shown in FIG. 1 that the chrominance C.sub.1 and C.sub.2 are compressed in time-base during every horizontal period in a line sequential manner and inserted into the horizontal blanking period of the luminance signal Y and then transmitted as a single composite signal illustrated in FIG. 18D.
When the band width of the signal transmission line is limited so as to effectively utilize the band width for the picture signal (the luminance signal Y and the chrominance signal C), a synchronizing signal (horizontal synchronizing HD) is inserted into the signal with the same polarity as the picture signal as is illustrated in FIG. 18D. The synchronizing signal cannot be detected and separated by level detection methods unlike, for example, an NTSC signal in the prior art but uses a frame synchronizing signal of a particular pattern which is inserted during every frame of a video signal and this pattern is detected so that on the basis of the frame synchronizing signal which is detected the horizontal synchronizing signal HD is detected at the timing of the horizontal period.
For this reason, when the above-described composite signal (TCI signal) with the synchronizing signal inserted therein is recorded and reproduced by video tape recorder, if a time-base fluctuation such as jitter occurs in the reproduced signal it becomes difficult to detect the horizontal synchronizing signal HD. Thus, it becomes impossible to time-base expand the chrominance signal on the basis of the horizontal synchronizing signal HD.
When a time-base correction (TBC) is intended to be accomplished for the reproduced signals, only the frame synchronizing signal can be used as a reference signal so that a time-base correction becomes very difficult to be accomplished and perfect correction becomes impossible.
Also, the detection and separation of the synchronizing signal requires the above-described procedures and a substantial amount of time is required until the synchronizing signal is detected. Particularly, when a so-called servo-control of the video tape recorder is carried out on the basis of the synchronizing signal upon playback a large amount of lock-in time is required.